Field of the Invention
The invention concerns a method for producing a honeycomb body, in particular a catalytic converter carrier body, having at least one stack of a plurality of at least partially structured metal sheets, and an apparatus for producing such a honeycomb body.
Carrier bodies for catalytic converters which provide for a reduction in the amount of pollutants in exhaust gases, in particular exhaust gases of an engine, can be in the form of a metallic honeycomb body. Such honeycomb bodies include a stack having a plurality of at least partially structured metal sheets. U.S. Pat. No. 4,923,109 describes a honeycomb body which has a stack of at least partially structured metal sheets, the stack being wrapped or twisted in opposite directions around itself and around a central region.
Published German Patent Application DE 195 21 685 A1, corresponding to U.S. Pat. No. 6,049,961, discloses a method for producing such a honeycomb body. In accordance with that method it is proposed that initially a stack is formed from a plurality of at least partially structured sheet metal layers. The stack is thereafter introduced into an open mould formed from mould segments corresponding to the outside shape of the honeycomb body to be produced, and the stack is held by a wrapping device in a central region. Thereupon the stack is wound or wrapped around in a direction of rotation and the mould is closed by pivoting the mould segments in the opposite direction to the direction of rotation of the wrapping device when a predetermined degree of wrapping is attained.
German Patent DE 195 22 327, corresponding to U.S. Pat. No. 6,029,488, discloses a method for producing a honeycomb body having a plurality of channels through which a fluid can flow. The honeycomb body has a plurality of at least partially structured sheet metal layers. This method is suitable in particular for producing a honeycomb body as is known from International Patent Application WO 90/03220. Such a honeycomb body has at least three stacks of metal sheets. At least three of the stacks are folded around a respective associated bend line in the central region of the honeycomb body and twisted in the folded condition in the same direction around each other and around the central region with the bend lines. Production of such a honeycomb body is effected in accordance with Published German Patent Application DE 195 22 327 A1 by virtue of each stack being folded about a respective bend line. The stacks when folded in that way are introduced into a mould. Each stack is held by a wrapping or twisting device in a central region. The wrapping or twisting device has winding bars which engage into the bent stack in the region of each bend line. The individual stacks are twisted in the same direction by rotation of the winding bars about a central axis.
International Patent Application WO 94/01661 discloses a honeycomb body which is made up of only a small number of metal sheets. The structure of the honeycomb body is suitable for at least one elongate electrical conductor to be integrated into at least one of the sheet metal layers or for one of the sheet metal layers itself to be in the form of an elongate insulated electrical conductor. For the production of such a metallic honeycomb body consisting of at least partially structured sheet metal layers, WO 94/01661 proposes that a hollow cone is produced from a small number of at least partially structured sheet metal strips. That hollow cone or circular ring is deformed from the outside inwardly at least at three lines so that a corresponding number of reversal lines are formed both in an outer region of the ring and also in an inner region thereof. The resulting star-like or rosette-like structure, which has loop configurations, is twisted by same-directional, rotational twisting of the loop configurations, which extend between the inner reversal lines and the outer reversal lines, about the inner reversal lines.
It has been found that defects, which adversely affect the quality of the honeycomb body, occur in some regions in the macrostructure of the finished honeycomb body. Such defects occur in an irregular fashion when successively producing a plurality of honeycomb bodies, which are manufactured using the same apparatuses. This requires particular measures in the quality control of the honeycomb bodies produced.